There is a conventional power supply unit that includes alternating-current (AC) power supply terminals to be connected to an AC power supply, a step-up inductor, a diode-bridge rectifier circuit, a switching device, a snubber circuit, and a smoothing capacitor, where the AC power supplied from the AC power supply has its voltage raised with the inductor and is converted into direct-current (DC) power in the rectifier circuit to be supplied to a load circuit.
By causing resonance current to flow through a closed circuit including multiple capacitors, multiple resonating reactors, and multiple diodes in the snubber circuit, the electric energy stored in the capacitors is regenerated to the smoothing capacitor.
Further in a power supply unit having a circuit configuration where the step-up inductor and the diode-bridge rectifier circuit are counterchanged, the AC power supplied from the AC power supply is converted into DC power in the rectifier circuit and has its voltage raised in the inductor to be supplied to a load circuit.
In this power supply unit, an inductor and a switching device are provided in the snubber circuit, and the electric energy stored in a capacitor is regenerated to the smoothing capacitor by turning ON/OFF the switching device in the snubber circuit.
For related art, reference may be made to, for example, Japanese Laid-open Patent Publication No. 11-018420 and Japanese Registered Utility Model No. 2605387.